Development of a granular normal contact force model based on a non-Newtonian liquid filled dashpot

Normal contact force models often suffer from a weak prediction of collisions between particles. They regularly fail to predict an adequate energy restitution behavior with increasing normal impact velocity. In particular, most non-linear models predict a net attraction force between two impacting particles near the end of a collision, which is unrealistic according to reported results. Such limitations have provided the impetus for the development of a normal contact force model that better predicts the unfolding of a collision between two particles. This model comprises a Hertz elastic force and a dissipative force that is evaluated by the motion of a non-Newtonian liquid in a dashpot. The model parameters are set using experimental restitution data for particle/particle and particle/wall contacts. In the current work, the measurement of energy restitution for particle/wall collision was carried out using several materials over a wide range of impact velocities, whereas particle/particle collision data were obtained from the literature. Model predictions for microscopic (e.g. particle velocity) and macroscopic (e.g. collision time) quantities are presented and compared with those from other non-linear models and experimental data. The model is observed to adequately predict the coefficient of restitution and to decrease the attraction force at the end of a collision.